In a typical cellular wireless network, a geographic area is divided into cell sectors. Each cell sector defines a geographic area in which wireless terminals (such as cellular telephones, personal digital assistants (PDAs) and/or other devices) operate. The wireless network normally has a base transceiver station (BTS) assigned to one or more cell sectors. The BTS produces a radio frequency (RF) radiation pattern over the one or more cell sectors. The RF radiation pattern allows the wireless terminals located in the one or more cell sectors to exchange signals with the BTS over an air interface.
The wireless network typically has a plurality of BTSs. The plurality of BTSs communicates concurrently with a base station controller (BSC) or the like that aggregates signals received from the plurality of BTSs. The plurality of BTSs and the BSC is commonly referred to as a base station. And the wireless network may have a plurality of base stations. The plurality of base stations in the wireless network is referred to as a base station system (BSS).
Each BSC in the wireless network may communicate with a packet gateway and a mobile switching center (MSC). The packet gateway and the MSC function to set up and connect calls with other entities. For example, the packet gateway may set up and connect calls with a server or other entity on an Internet protocol (IP) network, and the MSC may set up and connect calls with a telephone on a public switched telephone network (PSTN).
Generally, the BSC will assign a traffic channel respectively to each wireless terminal for transmitting and receiving signals over the air interface. Additionally, the packet gateway establishes a radio-packet (R-P) link with the BSC. The R-P link carries signals between the packet gateway and the BSC. The packet gateway establishes a separate R-P link for each wireless terminal in the wireless network, and in this regard, the signals carried by each R-P link are associated with a particular wireless terminal. The R-P link is referred to as the A10/A11 link in the code division multiple access (CDMA) network architecture.
In some instances, a server in the wireless network may send media, or “content,” to wireless terminals in the network. The content may represent information of interest to users of the wireless terminals, such as sports scores, weather reports, or advertising messages for instance. Alternatively or additionally, the content might comprise real-time streaming media such as voice or video conference content or broadcast television or radio signals. In any event, the server may transmit the content to one or more wireless terminals by inserting the content into one or more packets and transmitting the packets to the one or more wireless terminals.
If a server is going to transmit the same content to multiple wireless terminals (or for that matter to multiple network terminals of any kind), the server can unicast the content respectively to each terminal. That is, the server can establish a communication session respectively with each terminal and transmit a copy of the content to each terminal via the established unicast session with the terminal.
Unfortunately, however, one of the scarcest resources in a cellular communication system is the air interface between the BSS and the wireless devices. Typically, a given base station will operate at a designated carrier frequency, or at one frequency on the “forward link” (from the base station to wireless terminals) and at another frequency on the “reverse link” (from the wireless terminals to the base station). Communications in a given cell sector may then be divided into channels by spread-spectrum modulation and/or time-division multiplexing, for instance. However, a limited number of such channels will exist. Consequently, in a situation where multiple wireless terminals in a cell sector are all receiving the same unicast communication from a server, air interface resources in the cell sector can be depleted, which can adversely impact (e.g., block) other communications in the sector.
Another, more efficient way for a server to transmit the same content to multiple wireless terminals is to multicast the content. Multicasting essentially involves transmitting a single copy of the content to a multicast IP address and having all of the recipient terminals, or multicast group members, receive the transmission.
Using well known routing techniques, when content is transmitted to a multicast IP address, the content will be distributed to network nodes that serve multicast group members, and the nodes will then distribute the content to the group members. In cellular wireless communications, a wireless network may further maintain a multicast air interface link over which a base station can broadcast traffic destined to wireless multicast group members. Thus, to convey content from a multicast server to wireless terminals that are group members, the server may transmit the content to the applicable multicast IP address, network nodes may route the traffic to each base station system that serves members of the multicast group, and each base station system may then transmit the content over an air interface multicast link for receipt by group members that are in coverage.
To support multicast communications, under existing industry standards, a multicast server typically distributes to wireless terminals a “multicast channel listing” that specifies one or more multicast “channels” to which recipient wireless terminals can tune. (Alternatively, one or more multicast channels provided by various multicast servers could be cooperatively listed in a multicast channel listing generated by a wireless carrier or some other entity, and distributed to wireless terminals.) Each multicast “channel” represents a particular multicast group or multicast session having a corresponding multicast IP address (or the like) at which group members can receive associated multicast communications. The multicast channel listing generally specifies for each available channel a multicast “flow-ID” that can be used by a wireless terminal as a key to request membership in the multicast group, so that the terminal can then receive the associated multicast communications.
Since terminals may opt to tune to a given multicast channel at any time, the multicast server may regularly transmit content on each channel, just as broadcast television stations regularly transmit content on their channels. Upon tuning to a desired channel, a terminal may then begin to receive whatever content is currently being transmitted by the multicast server on that channel.
In practice, the multicast server or another entity may distribute the channel listing (e.g., by IP multicast communication) to various radio access networks or network entities, and base stations may then transmit the channel listing in an air interface paging channel message or other control channel message to wireless terminals in coverage. Upon receipt of the multicast channel listing, each wireless terminal may then store the channel listing for later reference by a user.
Thereafter, when a user of the wireless terminal is interested, the user may view the channel listing on a display screen of the terminal and may select a desired channel. In response, the wireless terminal may then transmit to the multicast server a JOIN request, seeking to join the multicast group that has the indicated flow-ID, and, after authenticating and authorizing the terminal, the multicast server may then provide the terminal with data that enables the terminal to receive and process the associated multicast communications. For example, the server may provide the terminal with the multicast IP address for the channel and with security information (e.g., a decryption key or the like), so that the terminal can receive and process packets destined to that multicast IP address, and thus receive and present the multicast communications on the selected channel.